Many emerging but non-validated indicators and biomarker thresholds have been used in the Relative Energy Deficiency in Sport (REDs) literature. Accordingly, we (1) compared the outcomes of the 2023 International Olympic Committee REDs Clinical Assessment Tool-version 2 (CAT2) (green, yellow, orange and red traffic light risk/severity assessment) with emerging REDs indicators, and (2) tested the utility of existing risk thresholds (clinical vs. subclinical biomarker cut-offs) for primary and secondary REDs indicators. Female (n = 143) and male (n = 70) athletes (performance tier 3-5) were assessed with the CAT2 and emerging REDs indicators featuring a self-report questionnaire, fasted blood analysis, resting blood pressure (BP) and heart rate (HR). Logistic regression was used to determine threshold cut-offs for blood biomarkers at which there was an 80% probability of REDs. Red-light athletes had significantly lower systolic BP (p < 0.001), HR (p = 0.009), white blood cell count (WBC; p = 0.018) and higher high-density lipoprotein cholesterol (p = 0.028) compared to green-light. Elevated cortisol: insulin ratio (p = 0.018), and reduced prolactin (p < 0.001) and luteinizing hormone (p < 0.05) concentrations were observed among higher-risk (orange + red) versus lower-risk (green + yellow) athletes. Males with total testosterone and triiodothyronine within the lowest quartile of reference range had an 80% probability of being classified as higher risk (orange + red) and history of BSI, respectively. For other outcomes at 80% probability, biomarkers were outside the clinical range. HR, systolic BP and WBC may be appropriate considerations for extreme (red-light) REDs diagnosis. More research with larger numbers of orange/red light athletes is needed to confirm findings and elucidate athlete-specific cut-offs for subclinically low biomarkers.

ABSTRACT Endurance competition preparation involves complex psychological, logistical, and sociocultural factors. This study investigated the pre‐race nutrition practices of female endurance athletes, by applying a newly developed extended Theory of Planned Behaviour, including behavioural execution to the framework to capture real‐world influences (ETPB‐X). Using a convergent mixed‐methods design, 27 female triathletes competing at the 2024 IRONMAN World Championships completed questionnaires, 48‐h food diaries, and semi‐structured interviews before and after the race. Quantitative data (n = 23) were analysed for energy and macronutrient intake, whereas qualitative data were thematically coded using the conceptual ETPB‐X framework, incorporating attitudes, subjective norms, perceived behavioural control (PBC), utilitarian drivers, and behavioural execution. Only 26% (6/23) of athletes achieved carbohydrate loading guidelines (8–12 g·kg−1 body mass (BM)·day−1), with an overall mean intake of 6.4 ± 2.1 g·kg−1 BM. Higher carbohydrate intake correlated with faster finish times (r = −0.50, p = 0.035), whereas fibre intake was positively associated with gastrointestinal (GI) symptom severity (r = 0.85, p < 0.001). Qualitative findings revealed that adherence to diet plans was influenced by PBC, travel logistics, emotional regulation, and athlete identity. This study provides a novel application of the ETPB‐X framework to pre‐race nutrition in female endurance athletes. Athletes often under‐achieve carbohydrate loading targets despite awareness, with success determined as much by psychosocial and contextual factors as by knowledge. Practically, enhancing PBC, improving planning/preparation, and delivering clear goal‐aligned education may bridge the intention‐behaviour gap. Integrating behavioural frameworks into performance nutrition offers a pathway towards more effective athlete‐centred interventions.

ABSTRACT:Moore, SR, Cantú, EI, Brantner, CL, Britton, ME, DelBiondo, GM, Blue, MNM, Bruinvels, G, Hackney, AC, Register-Mihalik, JK, and Smith-Ryan, AE. Using machine learning for identification of athlete availability predictors in a multisport elite female athlete cohort. J Strength Cond Res XX(X): 000-000, 2026-This study used machine learning to identify influential predictors (training load, recovery, wellness, body composition, and force plate jumps [FP]) of athlete availability (AA) in female athletes. Fifty-two National Collegiate Athletic Association Division I female lacrosse (n = 28) and soccer (n = 24) athletes were tracked across a season for AA (% of unmodified practices and games). Potential predictors included measures of training load (average max speed, top speed, distance, high-intensity running [HIR], acute to chronic ratios for distance and HIR), sleep recovery (duration, efficiency, resting heart rate, heart rate variability, and temperature), wellness (stress, soreness, mood, fatigue, sleep quality, and hormonal profile), body composition changes (lean mass, percent body fat, fat-free mass index, and bone mineral density), and preseason FP testing (reactive strength modified, eccentric mean braking, jump height, and peak power). Influential predictors were identified using elastic net regression. Goodness of fit was described with root mean squared error (RMSE). Root mean squared errors for combined, lacrosse, and soccer models were 17.8, 8.9, and 17.8%, respectively. Influential predictors of training load, recovery, and wellness variables were selected in all models, with differing impact between teams. Single-team analyses demonstrated inconsistent predictors; most notable contrasts included no FP variables selected for lacrosse AA, and no body composition variables selected for soccer AA. Differences in RMSEs and predictors between teams suggest single-team models as a stronger approach to understanding key outcomes for AA. Comprehensive modeling to identify athletes at risk of low athlete availability before injury would be valuable for practitioners to refine testing batteries and hone meaningful predictors to prioritize data streams.

Irisin is an exercise-induced myokine that has been proposed to exert beneficial effects on metabolic health. However, its response to different exercise training modalities in individuals with overweight or obesity remains inconsistent. This systematic review and meta-analysis primarily aimed to evaluate the effects of various exercise interventions on circulating irisin levels as the primary outcome in overweight and obese adults. Additionally, we assessed changes in other selected myokines and metabolic markers as secondary outcomes to provide a better understanding of exercise induced physiological adaptations. A systematic search was conducted in Web of Science, EMBASE, Cochrane Library, PubMed, SCOPUS, and Google Scholar (up to 22 April 2025) to identify randomized controlled trials (RCTs) evaluating the effects of different exercise training protocols (aerobic, resistance, concurrent, and high-intensity interval training) on circulating irisin levels in adults with overweight or obesity. The primary eligibility criterion to include studies was the measurement of circulating irisin. Within the RCTs meeting this criterion, we additionally extracted data on selected myokines (follistatin, myostatin, and FGF21) and metabolic markers (glycemic control and lipid profiles) when reported. These secondary outcomes were analyzed to contextualize irisin responses within broader metabolic adaptations, but no separate systematic search was performed for these variables. Pooled effect sizes were calculated using random-effects models and expressed as standardized mean differences (SMDs) with 95

Strength training (ST) is commonly implemented to enhance soccer-related fitness qualities such as sprinting, jumping, and changes-of-direction while also contributing to injury risk reduction. It is traditionally emphasized in the pre-season period. In-season ST may confer these benefits, but it can also induce muscle damage and inflammation. To examine the effects of a 12-week in-season ST program on maximal dynamic strength, muscle damage biomarkers, and inflammatory biomarkers, 24 elite young female soccer players (Tier 4 according to the McKay et al. classification) aged 14.9 ± 0.8 years and a maturity offset of +2.6 ± 1.1 years were randomly allocated to an ST group (STG, n = 12) or an active control group (CG, n = 12). Both groups followed the same soccer training program. However, in the STG, two weekly soccer sessions were replaced with ST. Overall training volume was comparable between groups. Maximal dynamic strength (1-RM tests for bench press, lat pull-down, and leg press), blood biomarkers of muscle damage (creatine phosphokinase [CPK], lactate dehydrogenase [LDH]), and inflammation (interleukin-6 [IL-6], tumor necrosis factor-α [TNF-α]) were assessed before (T1) and after (T2) the interventions. Analyses showed significant increases for STG for the 1-RM bench press, the 1-RM lat pull-down, and the 1-RM leg press (p < 0.001). No significant interactions were detected for any blood marker of muscle damage (LDH and CPK) or inflammation (IL-6 and TNF-α) (all p > 0.05). Results support a 12-week in-season ST program improved maximal dynamic strength in elite young female soccer players without altering resting levels of muscle damage or inflammatory markers measured 48 h after training compared to regular soccer training. These findings suggest that ST can be safely implemented during the competitive season in young female soccer players without overreaching or overtraining.

Low-energy availability (LEA) results in characteristic endocrine and metabolic adaptations, yet the contribution of carbohydrate availability (CA), defined as the difference between carbohydrate intake and oxidation during exercise, remains unclear. This randomized crossover study examined whether CA modulates endocrine and metabolic responses to LEA. Sixteen recreationally active adults (female, n = 9) completed two 4-day conditions of LEA [25 kcal·kg fat-free mass (FFM)-1·day-1] with low and high CA (1.5 vs. 4.0 g·kg-1·day-1). Diets were fully controlled, and participants performed daily exercise expending 20 kcal·kg FFM-1·day-1. Independent of conditions, LEA led to reductions in body mass (mean relative change: -1.3%; P < 0.001). High CA significantly attenuated the LEA-induced decline in insulin-like growth factor 1 (IGF-1; -22.9 ± 29.6 vs. -48.5 ± 26.2 ng·mL-1; P = 0.018). Insulin, leptin, and testosterone also exhibited greater decreases in low vs. high CA, although condition × time interactions did not achieve significance. LEA induced a shift toward greater fat oxidation at rest and during exercise, which was not modulated by CA but by sex. High CA mitigated reductions in submaximal and maximal blood lactate concentrations, indicating partial preservation of glycolytic function. Maximal performance indices (i.e., peak oxygen uptake and maximal power output) were neither affected by LEA nor by condition. These findings demonstrate that increasing CA under conditions of short-term LEA partially offsets endocrine responses, particularly the reduction in IGF-1, and attenuates reductions in blood lactate concentrations. Shifts in substrate utilization in response to LEA are largely independent of CA.NEW & NOTEWORTHY Low-energy availability (LEA) is often confounded by low carbohydrate availability. In a randomized crossover trial, we demonstrate that maintaining high carbohydrate availability (CA) during short-term LEA attenuates reductions in insulin-like growth factor 1 (IGF-1). In addition, we show that the modulatory effect of CA on changes in substrate utilization differs between sexes.

This paper synthesizes current research on women's football to develop comprehensive, evidence-informed nutritional strategies tailored to the specific demands of the sport. Four key themes are addressed: (1) energy requirements in women's football; (2) macronutrient and nutrient-timing applications around training and match play, including an illustrative case study; (3) supporting a player with inadequate energy intake, including an illustrative case study; and (4) nutritional considerations relating to fluctuations in female sex hormones. Rather than providing another descriptive narrative review, this synthesis translates research findings into practical strategies for implementation in real-world performance environments. Adequate energy availability is identified as a fundamental nutritional priority. Carbohydrate and protein intake are emphasized as essential for sustaining training quality, supporting recovery, and maximizing match performance. Nutrient timing is highlighted as a critical determinant of in-season performance and effective match preparation. Consideration is also given to the influence of hormonal fluctuations on thermoregulation and menstrual cycle-related symptoms, alongside nutritional strategies to mitigate these effects. This synthesis underscores the importance of individualized nutritional strategies to optimize health, performance, and return-to-play outcomes in women footballers.

Concentrations of female sex hormones fluctuate during the menstrual cycle (MC), while hormonal contraceptives (HC) generally suppress hypothalamic-pituitary-ovarian axis function resulting in lower concentrations of endogenous estradiol (E2) and progesterone (P4). Little attention has been paid to changes in androgen concentrations during MC and HC phases. Therefore, the aim of this study was to investigate changes in androgen concentrations over the MC and HC phases. The study was a cross-sectional analysis across MC and HC phases using four time points. E2, P4, follicle-stimulating hormone (FSH), luteinizing hormone (LH), total testosterone (tT), free testosterone (fT), sex hormone-binding globulin (SHBG), dehydroepiandrosterone (DHEA) and its sulfate (DHEA-S) were analyzed from the serum of healthy, physically active, naturally menstruating (NM = 36), hormonal intrauterine device using (IUD = 12) and combined HCs using (CHC = 25) females. In NM, concentrations of tT (β = 0.16, p = 0.050), fT (β = 1.85, p < 0.001) and DHEA (β = 5.29, p = 0.045) were significantly higher at ovulatory phase and concentrations of DHEA-S at the mid-follicular phase (β = 0.32, p = 0.012) compared to bleeding. In IUD, tT concentrations fluctuated significantly being highest at mid-cycle (β = 0.34, p = 0.001) compared to the sample defined as measurement 1 (based on bleeding and/or hormonal concentrations). In CHC, concentrations of E2, P4, tT, fT, DHEA, and DHEA-S remained unchanged between the HC phases. Since the endogenous hormonal milieu, including androgens, may affect female physiology, considering the fluctuation in androgen levels over the MC and HC phases may be of importance in physiological research.

Abstract This study examined whether low‐normal serum total testosterone (T) is associated with bone mineral density (BMD) or bone stress injuries (BSI) in male endurance athletes. Baseline data from 46 national‐ to international‐level Finnish athletes (age 24.8 ± 3.6 years; biathlon, cross‐country skiing, orienteering, triathlon, Nordic combined, endurance running) were analyzed; 31 completed 1‐year follow‐up. Participants were categorized into low T (lowest quartile: 11.8 ± 1.8 nmol/L) and normal T groups (17.9 ± 3.1 nmol/L; p < 0.001). At baseline, BMD and Z‐scores did not differ at any site (all p > 0.5), and BSI history prevalence was similar in low T (41.7%) and normal T groups (29.4%). The low T group had lower IGF‐1 (p = 0.031) but comparable cortisol and insulin. During follow‐up, repeated‐measures analysis showed a significant group‐by‐time interaction for T (p = 0.001), whereas 1‐year changes in BMD and Z‐scores did not differ between groups. Regression models showed that increased IGF‐1 independently predicted improved total body BMD (p = 0.01). In conclusion, low‐normal T in elite male endurance athletes was not associated with compromised bone health over 1 year and appeared largely reversible in the follow‐up subset.

ABSTRACT:Moore, SR, Joniak, KE, Ladan, AN, Britton, ME, Cantu, EI, Hirsch, KR, Hackney, AC, and Smith-Ryan, AE. Does hormonal phase affect acute high-intensity interval training exercise? An evaluation of performance and fatigue. J Strength Cond Res 40(9): e901-e908, 2026-Fatigue is a critical factor in high-intensity interval training (HIIT) performance, which may vary across female hormonal phases and with changes in work-rest ratio. This study evaluated exercise performance (average power [AP], peak power [PP]) and fatigue (power drop [PD; peak power-minimum power/time]) between 2 work-matched HIIT protocols during the low- (LHP) and high-hormone phases (HHP). In total, 35 women (age: 24.3 ± 6.1 years) completed 4 HIIT trials in randomized orders of hormonal phase and HIIT protocol: HIIT 1:1 : 10 rounds of 1 minute on/1 minute off; HIIT 2:1 : 20 rounds of 20 s on/10 s off. High-intensity interval training 2:1 resulted in significantly higher AP (HIIT 1:1 -HIIT 2:1 Δ-36.6 ± 2.3 W; p < 0.001) and PP (Δ-34.1 ± 4.0 W; p < 0.001) than HIIT 1:1 , with no significant difference between phase differences. When analyzed by protocol, HIIT 2:1 demonstrated greater PD in the LHP than in the HHP (Δ11.4 ± 4.7 W; p = 0.020), with no significant difference between phases for HIIT 1:1 . When collapsed across protocols, PD was significantly greater in the LHP than in the HHP (LHP-HHP Δ11.2 ± 4.9 W·s -1 ; p = 0.031). High-intensity interval training power performance (AP, PP) was influenced by the work-rest ratio, but not hormonal phase, with significantly higher power output in HIIT 2:1 . Greater PD during the LHP suggests physical fatigue may vary across hormonal phases, but the lack of HIIT 1:1 PD differences between phases may indicate augmented recovery with the equal work-rest ratio, particularly during the LHP. Although power performance was minimally different between phases, altering work-rest ratio may be a consideration for maintaining power outcomes and managing fatigue across female hormonal cycles, particularly in the LHP.

It is well-established that strength training (ST) improves physical fitness in young athletes. However, its specific effects on hormonal changes in female soccer players are unresolved. We examined the influence of a twelve-week ST program conducted twice per week on soccer-related measures of physical fitness and hormonal profiles in adolescent elite female soccer players. Twenty-four elite young female soccer players aged 15.3 ± 0.9 years (body-mass-index [BMI]: 20.8 ± 1.9 kg/m²) and Tier 4 training and performance caliber participated in this study. Players were randomly assigned to either an ST group (STG, n = 12) or an active control group (CG, n = 12). Several parameters were determined pre- and post-training including absolute and relative to kg body mass 1-RM in bench/leg press, countermovement jump (CMJ), linear sprint speed (5-m, 10-m, 30-m sprints), speed of changing directions (T-test with and without ball), sport-specific efficiency (Yo-Yo Intermittent Level1 [YYIRTL1]) and repeated shuttle sprint ability (RSSA). Cortisol (C), testosterone (T), growth hormone (GH), and insulin-like growth factor 1 (IGF-1) were assessed using blood samples collected after 12 h of fasting, before and after the ST program. No significant baseline between-group differences were observed. Statistically significant group-by-time interactions were found for muscle strength measures (e.g., relative 1-RM leg press, p = 0.046, d = 0.59), vertical jump performance (e.g., CMJ, p = 0.007, d = 1.28), and soccer-specific performance (e.g., RSSAMean, p < 0.001, d = 2.67). Post-hoc tests demonstrated significant increases for 1-RM leg press (p = 0.046, d = 0.59), CMJ (p = 0.007, d = 1.28), and RSSAMean (p < 0.001, d = 2.67) in STG. Furthermore, no significant group-by-time interactions were observed for hormonal markers (T, C, GH, and IGF-1; p > 0.05). While the ST program significantly improved physical fitness in adolescent female Tier 4 soccer players, no substantial changes were observed in hormonal markers. These findings suggest that ST-related physical adaptations observed in this population may not be directly linked to the hormonal markers measured in this study. Clinical trial number PACTR202504552619186 https://pactr.samrc.ac.za/Search.aspx Date of registration: 14/04/2025. “Retrospectively registered” Our study adheres to CONSORT guidelines.

Aim: Increasing female participation in elite sports has highlighted the need to better understand how intensive training affects reproductive health and sexual function. The aim of this cross-sectional study was to assess the prevalence of libido loss and sexual dysfunction in female climbers and to explore potential associations with low energy availability within the “relative energy deficiency in sports” framework. Methods: This is a cross-sectional multinational cohort study of female climbers as well as non-athletic controls from Switzerland, Germany, Austria, and Italy, to investigate female sexual function in athletes compared to a non-athletic control group from the general population through specific questionnaires, e.g., eating disorder screening (EDE-QS), sexual function (FSFI-d), low energy availability (LEAF-Q), and estrogen deficiency symptoms (MRS-II). A nonparametric procedure was used to check whether distribution differences between the groups were detectable. Where distributional differences were statistically detectable, selected parameters were considered as covariates in an analysis of covariance (ANCOVA). This has been carried out with the following covariates: LEAF- Q, MRS-II-score, age, BMI, and subjective satisfaction. Only participants without the signs of an eating disorder (normal EDE-QS scores) were included in this study. Results: A total of 173 women were included (elite: n = 31, amateur: n = 55, controls: n = 87). No significant differences in overall sexual function (FSFI-d total score) (p = 0.518) and libido (p = 0.610) were observed between groups in unadjusted analyses. However, after adjustment for relevant covariates, including MRS-II score and subjective sexual satisfaction, elite climbers demonstrated significantly lower FSFI-d scores compared to controls (p = 0.018). Notably, elite climbers reported higher subjective sexual satisfaction than controls (p = 0.002). Conclusions: While overall sexual function did not differ in unadjusted analyses, adjusted comparisons suggest that elite climbers may experience subtle differences in sexual function.

The purpose of this statement is to guide the design and conduct of high-quality sport and exercise science studies investigating the effects of varied ovarian hormone profiles on the health and athletic performance of elite female athletes. Beyond the menstrual cycle, these athletes present with a wide range of ovarian hormone profiles, including those associated with puberty and menarche, menstrual dysfunction, hormonal contraceptive use, pregnancy and postpartum, perimenopause, menopause and post-menopause. To effectively integrate knowledge of ovarian hormone profiles into high-performance sport and address the diverse needs of female athletes, future research and educational initiatives must encompass this broader spectrum of ovarian hormone profiles. However, to produce this knowledge, improvements in research design and conduct are necessary and can be facilitated by adopting reporting checklists as a structured approach to enhance transparency and reproducibility. We recommend that such quality assurance measures be integrated at the study design phase, along with clear research questions, appropriate study designs, and valid analysis methods. Consequently, the proposed guidelines aim to support researchers working in applied settings with elite female athletes in generating more robust and impactful evidence.

A better understanding of the practical and methodological challenges inherent in accurately tracking female hormonal status would enhance the clarity of research findings in exercise metabolism. The purpose of this study was to conduct an objective assessment of the quality of existing literature in this area and to provide a general overview of the practical conditions and issues encountered in studies investigating substrate metabolism during exercise in women, both in those using (HC+) or not using (HC-) hormonal contraceptives. Forty-four articles were identified through systematic reviews, meta-analyses, and searches on PubMed/MEDLINE. A quality assessment framework was developed and applied using a double-blind scoring approach. The loss/exclusion of data between baseline and final analyses per study was quantified, and the main challenges were highlighted. A higher mean global score was observed in studies conducted among HC+ women (81%) than those among HC- women (46%). Although the dropout rates were rarely mentioned in HC+ women articles, the mean rate of participant/data loss in HC- groups was 22.1%. The rate of HC- participant loss was positively correlated with the global score (r = .504, p = .02). High-quality research may be easier to achieve in studies involving HC+ women compared with those involving HC- women. Studies on HC- women seem to face more practical challenges, such as tracking the menstrual cycle and targeting specific (sub)phases of the menstrual cycle, along with technical and feasibility limitations. Thus, although the framework for designing such studies exists, the quality assessment of the available literature emphasizes its challenge in terms of research implementation.

Monitoring menstrual health has gained popularity in sports like football as an opportunity to identify recurring symptoms or adverse symptoms related to the menstrual or hormonal contraceptive cycle; to recognize challenges related to low energy availability (LEA), low carbohydrate availability, overreaching/overtraining, and/or overall lifestyle stress due to their association with menstrual disturbance/dysfunction; to be informative in contextualizing athlete training status, e.g., training load and performance progression; and to promote and empower body/health literacy and overall health in female athletes. Monitoring menstrual health may also offer valuable insights to inform decisions regarding training and recovery. In team sports like football, where training loads and match schedules are relatively uniform across the squad, individualized strategies to effectively manage recurring adverse symptoms or menstrual disturbance/dysfunction may be necessary to ensure that all athletes can perform and recover optimally. The purpose of this article is to describe the rationale and suggested approaches for tracking menstrual and hormonal contraceptive cycles (including menstrual disturbance/dysfunction) in field settings to facilitate monitoring of menstrual health to potentially contextualize the other health and performance data. Herein, we assess the feasibility and potential limitations of different tracking methods from traditional paper and pencil records to more sophisticated digital applications and biochemical measures for use in real-world settings.

Athletes may engage in weight cycling-successive episodes of weight loss and weight (re)gain-for performance reasons, but risk metabolic adaptations and regaining more fat that was lost (fat overshoot). This study aimed to assess the influence of a complete weight cycling episode on body composition, thermoregulation, and metabolism in athletes, considering sex and the type of sport practiced. Forty-eight athletes (28 males, 20 females) engaged in combat (n = 23), strength (n = 12), or endurance (n = 13) sports were examined under three experimental conditions (weight maintenance, weight loss, weight (re)gain) during a weight cycling episode using their habitual strategies. Body composition (dual-energy X-ray absorptiometry), core body temperature (telemetric temperature sensor), energy expenditure and substrate oxidation at rest and during moderate exercise (indirect calorimetry), and energy intake (48 h food record) were assessed. Overall, athletes lost 4.4 ± 2.3% body weight, 12.2 ± 10.6% fat mass, and 2.6 ± 2.3% fat-free mass (p < 0.001). All variables returned to baseline values during the regain period, and a higher fat mass regain was observed in endurance than combat athletes (p < 0.01). During weight loss, a transient increase in lipid and decrease in carbohydrate oxidation occurred at rest and during exercise (p < 0.001). Energy expenditure and core body temperature remained unchanged across the three experimental conditions, and no specific sex effect was observed. Overall, no apparent body weight nor fat overshoot was observed in athletes after a complete weight cycling episode. Nonetheless, the greater fat mass gain in endurance, compared with combat athletes, highlights a need for further specific long-term studies in this population. Clinical Trial registration: NCT04107545.

Endurance training potentially induces changes in resting energy expenditure (REE), body composition, and metabolic hormones, but well-controlled studies accounting for hormonal status of women are sparse on this topic. This study investigated how 8-week moderate intensity endurance training (MIET) affects these outcomes in recreationally active women. Naturally menstruating women (NoOC, n = 17) and combined oral contraceptive users (COC, n = 8) were assessed in the luteal/follicular phases and active/inactive phases before and after MIET. REE and respiratory exchange ratio (RER; by indirect calorimetry), body composition, estradiol, progesterone, free triiodothyronine (fT3), acylated and unacylated ghrelin were measured at rest. Linear mixed models with time, group, and their interaction were used to analyze the results in two stratified phase comparisons. No interaction effects were observed, but a main effect of time for RER was observed in the pooled sample, indicating a 5.6% increase (p = 0.004) at follicular/inactive phase. The COC group also had higher fT3 concentrations at all time points (p < 0.05). Two participants from different groups showed consistent ≥10% REE changes. An 8-week MIET did not induce detectable changes in REE, body composition, or metabolic hormones on a group level, but high individual variation was observed.

BACKGROUND:Despite growing interest in women's physiology in exercise sciences, the understanding of female athletes' energy metabolism remains limited. This study aimed to analyze substrate oxidation in response to energetic stimuli in female athletes using or not hormonal contraceptives, and to determine the influence of the estradiol-to-progesterone ratio fluctuations on energy metabolism. METHODS:Body composition (dual-energy X-ray absorptiometry), energy expenditure and substrate oxidation rates (resting, low-intensity walking exercise (4 km/h), and postprandial conditions; indirect calorimetry) were assessed among 32 athletes (23±3 years) during a high-training load period, in athletes using or not hormonal contraceptives (nine and 23, respectively). Athletes not using hormonal contraceptives were tested during high and low estradiol-to-progesterone (salivary samples) ratio conditions. RESULTS:No significant differences in energy metabolism at rest, whether fasting or postprandial, were observed between groups. During low-intensity exercise, a significantly higher net energy cost was observed in athletes using hormonal contraceptives (vs. high [P=0.01] and low [P=0.02] estradiol-to-progesterone ratio conditions). Higher carbohydrate (P=0.001) and lower lipid (P=0.005) oxidation rates were observed in the low estradiol-to-progesterone ratio condition compared with the high one in women not using hormonal contraceptives. CONCLUSIONS:Thus, endogenous and exogenous ovarian hormones may influence energy metabolism during low-intensity exercise in female athletes under high-training loads.